Round balers which are variously known as expandable chamber or variable volume type balers typically utilize cooperating sets of endless, flexible belts to form the baling chamber within the machine and to compress and roll the crop material into a bale as it is introduced into the chamber. These belts are driven longitudinally by one or more drive rolls and are also guided in their driven movement by a multitude of transverse idler rolls. The idler rolls are journaled by anti-friction bearings so that they rotate freely due to their engagement with the longitudinally driven belts, thus reducing frictional wear between the belts and the surfaces of the guide rolls. However, it has been found that when the belts and the idler rolls are moving together at the same velocities in this manner, there is a tendency for the rolls to wrap up with loose trash and stringy materials, causing plugging problems and other difficulties. From time-to-time the plugged and wrapped materials must be cleaned out of the machine to prevent malfunction and damage.